Oral Herpes (HSV-1, Herpes Simplex Virus-1) Causes

Herpes simplex virus (HSV) is a DNA virus that causes sores in and around the mouth. Two herpes subtypes may cause these sores.

Herpes simplex virus (type 1, herpes-1, or HSV-1) causes about 80% of cases of oral herpes infections. There is no evidence that HSV-1 viruses mutate into HSV-2 viruses.

Another herpes simplex virus (type 2, herpes-2 or HSV-2) causes the other 20% and causes the majority of genital herpes infections.

These viruses enter the body through small cuts, abrasions, or breaks in the skin or mucous membranes. The incubation period is about three to six days. Transmission of the virus is person to person and more likely to occur if blisters or lesions are present. The majority enter after an uninfected person has direct contact with someone carrying the virus (either with or without noticeable lesions). Simply touching an infected person is often the way children get exposed. Adolescents and adults frequently get exposed by skin contact but may get their first exposure by kissing or sexual contact (oral and/or genital contact), especially for HSV-2. Statistical studies suggest that about 80%-90% of people in the U.S. have been exposed to HSV-1 and about 30% have been exposed to HSV-2.

Oral lesions (and genital lesions) can reoccur. This happens because the HSV viruses are still alive but exist in nerve cells in a quiet, inactive (dormant) state. Occasionally, conditions in the body (see stage 3 above) allow the HSV to actively multiply, resulting in a new crop of lesions.

The HSV viruses multiply in the human cell by overtaking and utilizing most of the human cells functions. One of the HSV steps in multiplication is to take control of the human cell's nucleus and alter its structure. The altered nucleus (enlarged and lobulated or multinucleated) is what actually is used to help diagnose HSV infections by microscopic examination. The reason sores appear is because as they mature the many HSV particles rupture the human cell's membrane as they break out of the cell.

Transmission of HSV-1 occurs by direct exposure to saliva or droplets formed in the breath of infected individuals. In addition, skin contact with the lesions on an infected individual can spread the disease to another individual. Although close personal contact is usually required for transmission of the virus, it is possible to transmit HSV-1 when people share toothbrushes, drinking glasses, or eating utensils.